The present invention relates generally to semiconductor wafer fabrication systems, and to an improved method and apparatus for storing and loading semiconductor wafer carriers at a given semiconductor wafer fabrication tool.
The drive for reduced cost per unit wafer processed characterizes the semiconductor industry. Thus the semiconductor industry continuously searches for ways to increase wafer output and/or reduce overall equipment costs (costs of ownership). Among the factors significantly affecting cost of ownership for a given piece of equipment are clean room costs, footprint and labor costs. It is well recognized that overall semiconductor wafer fabrication system (i.e., fabrication tool) productivity increases are achieved by ensuring a constant supply of wafers at each tool. Conventionally this has been accomplished by employing a local buffer supply (i.e., a supply of wafers at the tool). For example, the xe2x80x9cMINI BUFFERxe2x80x9d marketed by Jenoptik/Infab is a vertical buffer which is positioned near a fabrication tool""s load lock chambers. The MINI BUFFER comprises a series of vertically arranged shelves and one or more load ports for access by the tool""s loader robot, and/or for access by factory transport agents (i.e., the mechanism that transfers wafer carriers from the factory to the buffer apparatus"" factory load port). Conventionally one MINI BUFFER is positioned near each load lock, a distance from the load lock sufficient to accommodate the axis of rotation of a front loader robot. The loader robot may then access either MINI BUFFER to obtain a wafer carrier for loading to either load lock. Although such methods maintain a constant local buffer supply of wafer carriers, they occupy a considerable amount of floor space thus increasing the system""s cost of ownership. The fact that fabrication tools are frequently maintained in a clean room environment further exacerbates the increased cost associated with the system""s larger footprint.
In addition, most prior art systems do not allow simultaneous access by the tool loader and the factory transport agent, and thereby complicate factory transport scheduling, and can result in throughput reduction.
Accordingly, there is a need for apparatuses and methods which can reduce footprint and/or increase machine/factory throughput.
In its broadest aspect the invention comprises a load/buffer adapted to provide local storage of wafer carriers at a fabrication tool, the load/buffer comprising a first factory load port adapted to receive wafer carriers to be transferred to and from the factory, a wafer carrier store, a first wafer carrier transfer mechanism adapted to transfer wafer carriers between the factory load port and the store, a first tool load port adapted to receive wafer carriers to be accessed by a fabrication tool, and a second wafer carrier transfer mechanism adapted to transfer wafer carriers between the tool load port and the store.
The wafer carrier store may comprise for example, a shelf, shelves, or a conveyor, and the wafer carrier transfer mechanisms may comprise for example, a shelf capable of raising or lowering the wafer carrier between the wafer carrier store and the load port (in which case rollers, a wafer handler or the like may transfer the wafer carrier between the shelf and the wafer carrier store), or a wafer handler capable of transferring the wafer carriers between the port and the store. The ports may be positioned at the height set by SEMI standard E15, or may be at a height greater than that of the fabrication tool, etc. The inventive apparatus may be positioned in front of the fabrication tool, beside the fabrication tool, at least partially above the fabrication tool, etc.
To enhance throughput, a plurality of load buffers may be connected so that one fabrication tool can receive a wafer carrier from the wafer carrier store of another fabrication tool if necessary. As used herein, the term xe2x80x9cfabrication toolxe2x80x9d includes any tool that performs a process on a substrate, whether it be deposition, etch, heat treatment, polish, clean, etc.
To further enhance throughput an inventive wafer handling method may be employed. The inventive wafer handling method increases throughput during any non-steady-state processing period (startup, tool failure, etc.), by dividing the wafers contained in a wafer carrier among a plurality of fabrication tools that are adapted to perform the same process. In this manner, each fabrication tool can immediately begin processing wafers, and throughput is greatly increased as compared to conventional methods which allow the entire wafer carrier full of wafers to remain with a single fabrication tool. Such conventional methods force the remaining fabrication tools to idle until a wafer carrier has arrived for each fabrication tool. Because most conventional fabrication systems deliver only one wafer carrier per hour, the inventive method results in a substantial increase in throughput. Although the inventive wafer handling method is most advantageously employed within a plurality of connected load buffers, such as those described herein, it may be used within any system containing a plurality of fabrication tools which perform the same process.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.